Expendable shotshell

ABSTRACT

An expendable cartridge made of thermoplastic material which is adapted to contain the necessary propellant, projectile charge, etc., and which is explosively expelled from the gun along with the projectile charge. There are several modifications of the invention, each of which requires some means to slit, fracture, or rupture the outermost cartridge structure, which then permits the inner structure to be released thus facilitating the ultimate final release of the projectile charge from the expendable cartridge, which then falls to the ground much like conventional shot containers.

Q United States Patent 1 1 1 3,741,122 Kordas, Jr. June 26, 1973EXPENDABLE SHOTSHELL 3,148,472 9/1964 Hegge et a]. 89/14 s13 [75]Inventor: Martin W. Kordas, Jr., Cos Cob, FOREIGN PATENTS ORAPPLICATIONS Conn- 1,449,850 7/1966 France l02/DIG. l 732,633 6/1955Great Britain 102/43 P [73] Asslgnee' :2??? g Cmnpmy 355,716 10/1961Switzerland 102/43 P r g 735,061 8/1955 Great Britain 102/43 P [221 1968OTHER PUBLICATIONS [21] Appl. No.: 755,649 Shotting Times-All PlasticWanda Shotshells by Wallace Labisky; November 1967. 52 U.S. Cl 102 43 P102 42 C, 102 43 C, l 1 l 1 Primary ExaminerR0bert F. Stahl 51 1111. c1.F42b 7/06 Lewis and Nidw'as Skwa" [58] Field of Search 102/38, 42, 42 C,

102/43, 43 P, 43 c T T An expandable cartridge made of thermoplasticmate- [56] References Cited rial which is adapted to contain thenecessary propel- UNITED STATES PATENTS lant, projectile charge, etc.,and which is explosively 3 577 921 5/1971 Langenhoven 102/38 expelledfrom the gun along with the projectile charge. 3:215:076 11/1965 Footeet There are several modifications of the invention, each 3,233,546 2/1966 Fume e 1 of which requires some means to slit, fracture, or rup-3,234,877 2/1966 Herter ture the outermost cartridge structure, whichthen per- 3,288,066 11/1966 Stadler et al mits the inner structure to bereleased thus facilitating 3,336,371 8/1967 Quinlan the ultimate finalrelease of the projectile charge from 3,345,945 10/ 1967 Quinlan et theexpendable cartridge, which then falls to the 35631562 1,1968 Stadler alground much like conventional shot containers. 3,444,777 5/1969 Lage3,485,170 12/1969 Scanlon 102/43 X 1 Claim, 14 Drawing Figures ,oppooPAIENTEDmuzs ms SBEHIWS Inventors- Martm W Kordas Jr.

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B KM Attorneg EXPENDABLE SHOTSHELL This invention relates to shotshellsfor firearms and in particular to expendable shotshell bodies designedto be expelled from the muzzle of the firearm along with the shot chargeor projectile as a result of the action of the explosive gases generatedby the burning propellant.

In recent years, considerable effort and expense have beenexpended--particularly by or for the military-to develop so-calledcaseless ammunition to replace the conventional brass or other metalcase cartridges. In addition to the decrease in weightand the decreasein volume, such caseless ammunition is attractive to the militarybecause they do not require metallic cases which must be recovered inthe field for re-use (particularly the larger artillery cases). Caselessammunition is also cheaper and can have real functional advantages. Forexample, because the entire cartridge is expelled from the gun, the gunsystem can be simplified over conventional guns which require elaborateextraction and ejection means. For purposes of this discussion,combustible cases, wherein the casing is made of a combustible material,are included with caseless ammunition.

The present invention relates to another approach which avoids some ofthe problems encountered with caseless ammunition and which enjoysalmost all of the advantages of caseless ammunition.

Caseless ammunition has not been widely accepted to date because ofcertain disadvantages which have not as yet been overcome. Thus,caseless cartridges are not waterproof, are structurally weak, and aresusceptible to premature or undesirable ignition due to cigarettes,cook-off in a hot gun chamber (especially automatic gun systems), andthe like. Solid propellants for such cartridges-have a tendency tobreakup when being handled or loaded, particularly in automatic orautoloading firearms. At present, dimensional control of the propellantis difficult and costly to attain and must be done by grinding ormachining.

The present velocities available in conventional ammunition, i.e., withmetal cases, have been limited by the pressure that can be containedsafely by existing guns and ammunition cases. In either a caseless orexpendable cartridge, the pressure and consequently the velocity is notlimited by the strength of a conventional case. It has long been, knownthat firearms can ,be'designed and made which will be able to withstandmuch higher pressures than presently made and limited by conventionalbrass cases. The limiting factor then becomes the gas seal which mustreplace the obturating function now being performed by the metal cases.

. The present invention provides an expendable plastic shotshell case orbody which is expelled from the muzzle of the firearm along with theshot or other projectile. The plastic body protects the propellantduring storage and handling from moisture, unintentional ignition aswell as providing structural rigidity. An expendable cartridge made fromsuch a body is only slightly heavier than equivalent caseless ammunitionbut on the Another object of this invention is to provide a cartridgehaving a body which is expelled from the muzzle other hand, it avoids orsubstantially minimizes the 1 problems mentioned above.

It can be seen that the major object of this invention is to provide anexpendable shotshell having substantially all of the advantages ofcaseless ammunition and having none of certain of its disadvantages.

of a firearm.

Still another object of this invention is to provide a cartridge thatprotects the propellant from its environment during storage and handlingbut which leaves no casing in the firearm chamber to be extracted afterfirmg.

A further object of this invention is to provide a cartridge that has acase which provides a thermal barrier against accidental ignition andprovides sufficient strength for use in automatic or autoloadingfirearms while leaving no case to be extracted after firing.

Still a further object of this invention is to provide a cartridge witha body that contains propellant and priming means as well as projectilemeans, which body is expelled through the muzzle of a gun.

An additional object of this invention is to provide an expendable bodyshotshell having a separate pre-slit shot container and a gun barrelhaving means therein to strip the body away from the pre-slit shotcontainer, thus facilitating releasing of the projectiles after theshell leaves the muzzle of the firearm.

A still additional object of the invention is to provide an expendablebody cartridge having a pre-slit projectile chamber and afrangible bodycover designed to rupture or fracture upon firing, thus facilitatingrelease of the projectile after the shell leaves the muzzle of the gun.

Other objects will be apparent from the specification and drawings inwhich:

FIG. 1 is a sectional side elevation of one form of expendable body forthe cartridge which is the subject of this invention shown in positionin a firearm chamber;

FIG. 2 is a sectional side elevation of the form of expendable bodyshotshell loaded with solid propellant which is shown in FIG. 1;

FIG. 3 is a sectional side elevation of an expendable body shotshell ofthe type shown in FIG. 2 loaded with loose or granular propellant heldin place by a molded propellant disc;

FIG. 4 is a sectional side elevation of an expendable body shotshell ofthe type shown in FIG. 2 modified to provide a snap lock groove means atthe front end of the body to secure the shot protector to the body;

FIG. 5 is a sectional side elevation of a portion of an expendable bodyshotshell showing a snap lock groove means provided at the rear of theprojectile chamber to secure the shot protector to the body;

FIG. 6 is a sectional view of an alternate form of expendable bodyshotshell shown in position in a shotgun chamber;

FIG. 7 is a sectional side view of an expendable body with thecushioning means integrally formed with the body;

FIG. 8 is a sectional side view of an expendable body shotshell whereinthe shot containing chamber is closed off by a top wad snapped intoplace within the body;

FIG. 9 is a sectional side view of a modified expendable body shotshellwhere the body includes an integral hinged shot containing portion whichis retained in place by means of a separate retaining sleeve;

FIG. 9A shows a top view of the cartridge shown in FIG. 9;

FIG. 10 is a sectional side view of a type of expendable cartridgehaving a frangible cover member which fits on the outside of the bodyand over the shot chamber;

FIG. 11 is a sectional side view of a modified design where thetransverse wall means is solid and a separate cushioning wad is providedinside the shot chamber;

FIG. 12 shows a modification of the expendable cartridge shown in FIG.in which the transverse wall means is solid; and

FIG. 13 shows another modification of the expendable cartridge in whichthe body shot protector is eliminated and the frangible cover is thesole shot container in this modification.

Referring now to the drawings, FIG. 1 illustrates one form of anexpendable body 10 for a cartridge 12 positioned in an associated gun 14before firing. It should be understood that although the drawings showsthe invention incorporated in a shotshell, it is intended that theinvention applies equally to other conventional projectiles such asso-called rifled slugs and industrial slug loads, etc. For the sake ofconsistency, all further reference in this specification will be to ashotshell load.

Body 10, and corresponding bodies in modifications described later, canbe made by injection molding, cold-forming, or any other conventionalmethod of making plastic articles. Although generally any grade ofolefinic polymer or co-polymer can be used, polyethylene is especiallysuitable for use in the body. Other plastics which are suitable are ABSand ABS alloys (TERPOLYMER OF ACRYLONITRILE, BUTADI- ENE AND STYRENE),flexible vinyls, polyamides, cellulosics, polycarbonates, and othershaving suitable impact properties.

Body 10 comprises a tubular member 16 and an imperforate, transversewall or web member 18, which divides the tubular member 16 into tubularwall portions and 22. (See FIG. 2). Transverse wall 18, together withtubular wall portions 20 and 22, define an openended, forward shotcavity or chamber 24 and an openended, rear propellant cavity or chamber26, respectively. Wall member 18 must be substantially imperforate inorder to insure that the full thrust of the explosive gases, generatedin the propellant chamber after ignition of propellant 28, is directedto propel the body 10 through the gun barrel 30. The explosive gasescannot be permitted to enter the shot chamber 20 where it might melt theshot pellets or affect their trajectories. The intersection of web 18and tubular wall portion 22 is formed as a radius 32 to avoid a stressriser that would cause the web to be blown or sheared out on fir-Propellant means 28 for the present invention can be either a moldedone-piece solid propellant, loose or granular propellant, liquid, orgelled. FIGS. 1 and 2 show the use of a one-piece molded solidpropellant 28 in which a recess (not numbered) is formed in which aprimer cup 34 is positioned and secured by any wellknown means. Primercup 34 also has a recess (not numbered) in which a primer 36 (eitherloose or molded) is secured. Primer cup 34 is made of solid propellantwhich may or may not be the same propellant as the main propellantcharge 28-depending on the desired ballistics. The main propellantcharge 28 is held in propellant chamber 26 by an interference fit, by anadhesive, or by any other conventional means. Primer cup 34 and primer36 can be similarly secured to the main propellant charge. Obviously,the primer cup can be eliminated and the primer inserted directly in apocket formed in the main propellent charge (See FIG. 7).

Primer 36 is covered by foiling paper (not shown) or other suitablemeans and the propellant-primer assembly is sealed by a thin film ofsuitable plastic 38 which can either be fastened with an adhesive orheat-sealed to body 10. Altemately, coatings such as epoxy, can be usedto seal the primer-propellant assembly.

A rim or shoulder 40 is formed on the outside diameter of the body 10 toprovide a surface for head spacing and support against the firing pinblow. Sufficient restraint is provided to hold the shell back forefficient propellant ignition and burning but restraint is low enough sothat the shoulder 40 will release before peak pressure is reached andthe entire shell will be expelled from the muzzle.

Although the drawing shows various ways of confining the shot pellets 42in shot chamber 24, FIGS. 1 and 2 show the use of a shot protector 44which functions as a shot container as well as the closure means for thecartridge. Shot protector 44 is preferably made of plastic material andincludes a tubular side wall portion 46 which is open at its rear endand closed off by a transverse closure wall 48 at the mouth or front endthereof. Slit means 50 are provided across the closure wall 48 andextending down the tubular side wall to a point adjacent the open endbut falling short a predetermined distance to provide an unslit portion52 which functions as a hinge means, as explained later. A small unslitportion (not shown) may also exist at the center of the front face tosecure the multiple sections together at the front, thus holding theshot in place until firing. Shot protector 44 is slidably positioned inthe shot chamber 24 and secured therein by any well-known means, such asan interference fit, which would be the cast in FIGS. 1 and 2.

The preceding discussion has referred to the modification shown in FIGS.1 and 2. However, various modifications can be made to this cartridgedesign within the meaning of the invention.

FIG. 3 shows an expendable cartridge similar to the one shown in FIG. 2with some modifications. One change is that the supporting rim orshoulder 40a extends further to the front than the shoulder 40 shown inFIG. 2.

Other ways in which FIG. 3 differs from FIG. 2 are that primer 36 ispositioned and secured to a pelletized powder disc 54 which holds loosepropellant powder or granules 56 in propellant chamber 26. Groove 58 isformed at the rear end of body 10 and extends inwardly into thepropellant chamber so that a cooperating rim 54a on disc 54 can besnapped into holding relationship therewith.

FIG. 4 shows a solid molded propellant 28a positioned in the propellantchamber and a primer 36 positioned in a recess (not numbered) in thesolid propellant 28a. This figure also shows the use of a groove 60located at the front end of the tubular side wall 46 which cooperateswith a corresponding locking rim 62 on the forward end of the shotprotector 44 to lock the shot protector within the shot chamber. Aforwardly extending rim or foil 64 may be located on the shot protectorto assist in opening up of the shot protector after it is expelled fromthe muzzle of the gun.

FIG. 5 shows a similar interlocking means to that shown in FIG. 4 exceptthat the groove 60a and locking rim 62a are positioned at the rear endof the shot chamher.

The preceding discussion has related primarily to the expendablecartridge. However, this type of ammunition requires redesigning ofconventional firearms to be able to fire the ammunition. FIG. 1 showsthat gun barrel 30 has a longitudinal bore 66 through which theprojectiles and the cartridge case are explosively propelled. A gunchamber 68, formed in the rear or breech end of the barrel, has aninwardly projecting abutment 70 which acts as a locating and stop meansfor shoulder 40 of the expendable cartridge. The position of thisabutment 70 locates the cartridge in the gun chamber and providesnecessary support to the cartridge so that the primer can be ignited bythe firing pin 72 which conventionally moves slidably through the gunbolt 74. A gas seal 76, of the type shown in US. Pat. No. 3,166,864,issued on Jan. 26, 1965 to J. J. Scanlon, Jr., is shown in FIG. 1between the gun bolt and the chamber to prevent the explosive gases fromescaping through the rear of the gun barrel and out the receiver. Asimilar sealing'system 72a is also used to seal the firing pin.Obviously, any type of gas seal can be used for the gun bolt and thefiring pin.

Located as'part of the barrel adjacent the front end of the cartridgewhen the cartridge is in position in the gun chamber are cutters orlands 78. These cutters 78 can be full length or short and are designedto be impacted by the explosively projected cartridge. The cuttersfunction to cut or fracture the tubular wall portion 20 of the shellbody in a plurality of places. Once cut the shell body opens up or peelsback after being explosively expelled from the gun barrel much likeconventional shot containers. The shot protector 44 and the enclosedshot are thus freed from the body so that the shot protector can open uplike a clam (because of the slit means 50 and hinge means 52) to permitthe shot pellets to proceed towards the target without interruption.

The clam closure can be molded to provide built-in stress to assistopening. As molded, the part would be in a partially open position. Onloading the part would be forced to a closed position thereby causingstress in the part that will cause it to open when restraint is removed.

It is preferable to locate the cutters 78 near the gun chamber or theorigin of the bore where the velocity is minimum since it is known thatsabot cutters placed near the muzzle are damaged by the high velocities.

An alternative version of the expendable cartridge discussed above isshown in FIG. 6. This modification shows a plastic body 100 withtransverse wall or web 118 separating the body into a shot chamber 124and a propellant chamber 126. integrally formed with the body 100 andextending radially is a ring seal 140 located adjacent web 118, whichforms an obturating seal and is positioned in a circumferential recess180 of gun bolt 174 and clamped against chamber abutment 170. Uponfiring, the ring 140 is sheared off body 100 and remains in the gunafter the rest of the cartridge is expelled from the gun barrel. Theobvious drawback of this modification is that the sheared-off ring 140must be extracted and ejected from the gun. This modification does givegood predetermined restraint force based on the shear strengthof theplastic.

The expendable case shot shell shown in FIG. 6 can be made to functionso that the rim 140 and the body remain intact during firing andcompletely exit the bore. This can be done by providing some clearancebetween the rim and the chamber so that the rim is not clamped andproviding a chamfer at the front of the rim so that the rim will beforced down instead of being sheared off.

FIG. 7 shows an expendable cartridge similar to the one shown in FIG. 2except that the body 200 has transverse wall or web 218 including anintegrally formed cushioning section 282. Obviously, the cushioningsection can be made in a variety of designs and can be lengthened orshortened depending on the load of pellets and/or propellant desired.

FIG. 8 shows another modification wherein a body 300 has a transverseweb 318 which with the body defines shot chamber 324 and propellantchamber 326. The propellant and priming means are similar to themodification shown in FIG. 3. Differing from FIG. 3 is the method ofclosing off the shot chamber and containing the shot charge 342 therein.Tubular wall 320 of body 300 includes a circumferential groove 384 inwhich a top wad 386 is snapped in place. Top wad 386 is preferably madeof some frangible material which will disintegrate upon firing so as toavoid obstructing the flight of the shot charge. It can be appreciatedthat a shot container can be utilized with this modification. Either ashot cup or combination shot chamber-wad column can be inserted withinthe shot chamber 324.

FIG. 9 shows a further modification of an expendable cartridge. Thismodification shows a one-piece plastic body 400 having an integral web418 which, with body 400, defines shot chamber 424 and a propellantchamber 426. Shot chamber 424 is defined in this modification bytransverse web 418, tubular side wall portion 420, and an integrallyformed transverse closure wall member 488. As can be seen in FIG. 9A,the closure wall 488 has a plurality of transverse slits 490 whichextend longitudinally down the tubular side wall 420 as slits 490a andthen circumferentially at the lower end of the shot chamber as slits490b. This arrangement of slits is effected by molding a plurality ofsegments (any number can be made 2, 4, etc.), like flower petals, sothat when closed, they form a cylinder closed at the front. The unslitportions 492 actually hold the segments to the transverse web 418 andare the link which makes the tubular side wall 420 integral with therest of the body. In loading the cartridge, the shot charge is placed inthe end formed by the segments with the segments spread to form aconical shape. The segments are drawn closed to form a cylinder whichencloses the shot and a plastic sleeve 494 is slipped over the segmentedwall portions to retain the shape and complete the shell assembly. Onfiring, sleeve 494 will be cut by the body cutter or land 78 (FIG. 1) toremove the restraint effected by the sleeve so as to permit the releaseof the shot in flight from the muzzle. Alternately, sleeve 494 may be ofa frangible plastic, and removed from the body by the shock of firing.

As with the other modifications, cushioning means can be provided bymolding a collapsible section in the shell body similar to conventionalshotshell wads or by inserting a separate cushioning material, such asfelt, cork, or plastic foam within the shot chamber under or to the rearof the shot charge. (See reference numeral 599 in FIG. 11).

A different design principle is illustrated in FIG. 10, i.e., shotrelease by shattering or complete breakup of a portion or all of theshot containing part of the shell by the shock of firing and/or forcesexerted by an abutment or by a constriction in the gun bore.

FIG. 10 shows a gun barrel 530 having a longitudinal bore 566 with afirst chamber abutment 570 which functions in the same manner asabutment 70 in FIG. 1. Second abutment 596 is located in the gun boreadjacent to the front end of expendable cartridge 500, which is shown inposition for firing in FIG. 10.

Cartridge 500 includes a molded plastic body 510 having an integrallyformed transverse wall means 518 which, with body 510, defines a shotchamber 524 and a propellant chamber 526. Wall means 518 includes acushioning section 582 integrally formed therewith similar to theshowing in FIG. 3.

The propellant chamber 526 etc., are similar to the showing in FIG. 3and need not be repeated here. There are differences, however, in theshot chamber and closure thereof.

Shot chamber 524 is defined at its rear by the transverse wall means 518and at its sides by tubular body side wall portion 520 which isintegrally formed with the wall means 518. A plurality of slits 590 inside wall 520 extend longitudinally to the mouth end thereof to form aplurality of wall segments much like conventional shot containers in usetoday which are adapted to pull back and release the shot pelletsenclosed therein after being expelled from the muzzle of the gun.Closing off the open end of the tubular side wall portion 520 is afrangible cup-shaped cover 598 which fits over the segmented side wall520 to hold it in shape and retain the shot therein. The rear end of thecover 598 is secured in some manner, e.g., an interlocking groove (notshown) in the forward face of transverse wall 518. Obviously, othermethods of attaching the cover 598 to the body 510 can be utilized.

Upon firing, the cartridge 500 reacts in the same manner as previouslyexplained. When sufficient pressure has built up (almostinstantaneously), the shoulder 540 will release and the entire cartridgewill move forward in the gun chamber. When the forward end of theexplosively propelled cartridge impacts at relatively low velocityagainst abutment 596-or at a greater velocity against a conventional gunchoke, the frangible cover 598 will break up whereupon the segmentedside wall portion 520 will be free to open up upon being expelled fromthe muzzle.

Although abutment 596 is shown adjacent the chamber, it should beappreciated that the abutment may be located anywhere down the gun bore.Also, a tapered bore restriction (not shown) may also be successfullyemployed.

Cover 598 is made of a frangible plastic which will provide adequatestrength for handling but which will break up upon firing. Amongmaterials which would be suitable are polystyrene, rigid vinyls,polyamides, cellulosics, acrylics, chlorinated polyether, phenoxy,polysulfone, and thermosetting plastics such as phenolics, melamines,ureas, alkyds, polyesters, allylics, etc.

Shoulder 540 constitutes a special feature of the design. In addition tothe restraint feature, i.e., holding the shell in the chamber afterfiring until sufficient pressure is built up, etc., the shoulder alsoserves as an obturator gas check and a means to clean the bore. Thispart of the shell, i.e., the shoulder 540, is made of polyethylene orsome non-frangible material. Because it remains intact during firing andit is larger than the bore, it will sweep the bore clean of particlesleft by the frangible part of the shell and any powder residue frompreceding shots.

FIG. 1 1 shows a modified expendable cartridge of the type shown in FIG.10. This modification shows a solid transverse wall 518a and a separatecushioning wad 599 positioned under the shot charge 542 and within theshot chamber 524.

FIG. 12 shows the loaded expendable cartridge shown in FIG. 10 butwithout the gun details and without the integral cushioning section inthe transverse wall means.

FIG. 13 shows a modified expendable cartridge similar in some respectsto that shown in FIG. 10 except that the tubular side wall portion 520is omitted. The frangible cover 598 is the sole shot container in thismodification. Obviously, this design loses some of the shot protectingand gun bore protecting advantages found in shot containers since thefrangible cover will break up upon firing so that there will be littleor no plastic between the shot charge 542 and the gun bore during thetime the shot is travelling through the gun bore.

What is claimed is:

1. A cartridge casing adapted to be completely expelled from the muzzleof a firearm, said casing comprising: a tubular plastic body having aninterior and an exterior; transverse wall means fixed to and extendingacross the interior of said body; and an enlarged portion on theexterior of said body forming shoulder means thereon, said shouldermeans being closely laterally adjacent to said wall means, and saidshoulder means tapering outwardly and longitudinally along said body,said shoulder means being operative to initially resist forward movementof said casing when chambered and fired, and said shoulder means furtherbeing operative, upon development of a predetermined chamber pressure,to subsequently permit said casing to be propelled substantially intactthrough a firearm muzzle.

i 0 i i t mg f UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTIONPatent No 3,741,122 (D-46) Dated. Jane 26,' 1973 Inve tor) MARTIN w.KORDAS, JR.

It is certified that error appears in the above-identified patent madthat said Letters Patent are hereby corrected as shown below:

' r Col. .6, Line' 2 7, "chamber" should read"'conta1ner-.

Signed and sealed this 17th day of September 1974.

McCOY M. GIBSON JR. 'c. MARSHALL DANN- Attesting Officer Commissioner ofPatents NS/pkh 2-27-l974.

32 3 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent: No.741,122 D-46) Deted. Juhe 26, 1973 Inventor-(s) MARTIN w. KORDAS, JR.

It is certified that error appears in the above-identified patent shownbelow:

and that said Letters Patent are hereby corrected as Col. ,6, Line 27,"chamber" should read -container-.

Signed and sealed this 17th day of September 1974.

MOY M. GIBSON .JR. C. MARSHALL DANN Attesting Officer Commissioner ofPatents NS/pkh 2-27-l974.

1. A cartridge casing adapted to be completely expelled from the muzzleof a firearm, said casing comprising: a tubular plastic body having aninterior and an exterior; transverse wall means fixed to and extendingacross the interior of said body; and an enlarged portion on theexterior of said body forming shoulder means thereon, said shouldermeans being closely laterally adjacent to said wall means, and saidshoulder means tapering outwardly and longitudinally along said body,said shoulder means being operative to initially resist forward movementof said casing when chambered and fired, and said shoulder means furtherbeing operative, upon development of a predetermined chamber pressure,to subsequently permit said casing to be propelled substantially intactthrough a firearm muzzle.